Evaluating the Effect of Grouting on the Strength of Foliation of Metamorphic Rocks

The mechanical properties of metamorphic rocks are affected by foliation, which induces apparent anisotropy and heterogeneity. In this study, a series of pull-off and direct shear tests were performed to investigate the tensile strength, peak shear strength, and residual shear strength of the foliation in different metamorphic rocks (HY slate, RS schist, and SH schist). In addition, the effect of grout reinforcement on the fractured foliation was evaluated. Finally, a model was proposed to evaluate the shear strength of the cement-grouted foliation. The key findings of this study included the following: (1) The tensile and shear strengths of the schists were higher than those of slate. A nonlinear failure criterion for the foliation was adopted to reasonably describe their failure envelopes. (2) For the long-displacement shear tests, the friction angle of HY slate increased as the number of shearing cycles increased, and the friction angle of schists slightly decreased, which was related to the surface variations of the rocks. (3) Considering the grout reinforcement on the fractured foliation, the low strength of the grouted slate was attributed to the weak interface bonding between the cement and slate. In contrast, the strength of the grouted schists significantly increased. The high roughness strongly contributed to the grout reinforcement on the schist foliation. (4) Our proposed shear strength model for cement-grouted metamorphic rocks, which considered factors such as the joint roughness coefficient, uniaxial compressive strength of cement, residual friction angle, and interface tensile strength, provided reasonable predictions that aligned with the experimental test results.